ISL8483 Intersil Corporation, ISL8483 Datasheet - Page 10

• Manufacturer Part Number: ISL8483
• Description: 5V/ Low Power/ High Speed or Slew Rate Limited/ RS-485/RS-422 Transceivers
• Manufacturer: Intersil Corporation

In point-to-point, or point-to-multipoint (single driver on bus)
networks, the main cable should be terminated in its
characteristic impedance (typically 120Ω) at the end farthest
from the driver. In multi-receiver applications, stubs
connecting receivers to the main cable should be kept as
short as possible. Multipoint (multi-driver) systems require
that the main cable be terminated in its characteristic
impedance at both ends. Stubs connecting a transceiver to
the main cable should be kept as short as possible.
Built-In Driver Overload Protection
As stated previously, the RS-485 spec requires that drivers
survive worst case bus contentions undamaged. The
ISL84XX devices meet this requirement via driver output
short circuit current limits, and on-chip thermal shutdown
circuitry.
The driver output stages incorporate short circuit current
limiting circuitry which ensures that the output current never
exceeds the RS-485 spec, even at the common mode
voltage range extremes. Additionally, these devices utilize a
foldback circuit which reduces the short circuit current, and
thus the power dissipation, whenever the contending voltage
exceeds either supply.
Typical Performance Curves
FIGURE 6. DRIVER OUTPUT CURRENT vs DIFFERENTIAL
90
80
70
60
50
40
30
20
10
0
0
OUTPUT VOLTAGE
DIFFERENTIAL OUTPUT VOLTAGE (V)
1
ISL8483, ISL8485, ISL8488, ISL8489, ISL8490, ISL8491
2
10
3
V
CC
4
= 5V, T
A
= 25
5
o
C, ISL8483 thru ISL8491; Unless Otherwise Specified
In the event of a major short circuit condition, ISL84XX
devices also include a thermal shutdown feature that
disables the drivers whenever the die temperature becomes
excessive. This eliminates the power dissipation, allowing
the die to cool. The drivers automatically reenable after the
die temperature drops about 15 degrees. If the contention
persists, the thermal shutdown/reenable cycle repeats until
the fault is cleared. Receivers stay operational during
thermal shutdown.
Low Power Shutdown Mode (ISL8483 Only)
These CMOS transceivers all use a fraction of the power
required by their bipolar counterparts, but the ISL8483
includes a shutdown feature that reduces the already low
quiescent I
whenever the receiver and driver are simultaneously
disabled (RE = V
600ns. Disabling both the driver and the receiver for less
than 50ns guarantees that the ISL8483 will not enter
shutdown.
Note that receiver and driver enable times increase when
the ISL8483 enables from shutdown. Refer to Notes 5-8, at
the end of the Electrical Specification table, for more
information.
FIGURE 7. DRIVER DIFFERENTIAL OUTPUT VOLTAGE vs
3.6
3.4
3.2
2.8
2.6
2.4
2.2
3
2
-40
CC
TEMPERATURE
to a 1nA trickle. The ISL8483 enters shutdown
-25
CC
and DE = GND) for a period of at least
TEMPERATURE (
0
R
DIFF
25
= 100Ω
o
C)
50
R
DIFF
= 54Ω
75
85